Identifier

etd-04172012-145151

Degree

Doctor of Philosophy (PhD)

Department

Renewable Natural Resources

Document Type

Dissertation

Abstract

Floodplains forests are productive and diverse ecosystems characterized by frequent riverine flooding. Levees and dams have eliminated or altered riverine flooding which can potentially affect floodplain tree recruitment and growth. Increased light availability from canopy disturbances may increase photosynthesis given sufficient soil moisture, but information on the combined effect of canopy disturbances and hydrologic modifications on tree recruitment and growth is lacking. I used dendrochronological techniques to reconstruct tree recruitment, growth (Quercus lyrata, Fraxinus pennsylvanica), and canopy disturbance patterns over a 90-year period at several floodplains in the Mississippi River Alluvial Valley, USA: an unleveed site below dams and two sites within a ring levee. At the site below dams, flood frequency increased in the late non-growing season during the post-dam period, but decreased in the late growing season, although stage may have kept water in the root zone. Mean flood duration of pre-dam and post-dam periods was similar. Interannual variability in flooding may have resulted in recruitment of tree species of varying flood tolerances. Recruitment of shade-tolerant species (Celtis laevigata, Ulmus americana) was common during periods of infrequent canopy disturbances, but recruitment and growth of moderately shade-tolerant species such as F. pennsylvanica increased following widespread canopy disturbances. Unlike Q. lyrata, F. pennsylvanica had positive relationships with river stage during the late growing season in the post-dam period, suggesting riverine influence via groundwater links. At sites within a ring levee, flooding was short duration with longer duration flooding at lower elevations due to ponding of precipitation. Recruitment of flood-intolerant species such as C. laevigata expanded after levee construction except at lower elevations where recruitment of flood-tolerant species such as Q. lyrata followed canopy disturbances. In the post-levee period, growth of Q. lyrata and F. pennsylvanica was closely correlated with surface soil moisture and increased following canopy disturbances. Growth maintained strong relationships with spring stage at low elevations despite the elimination of overbank flooding, suggesting riverine influence via groundwater links. Results of my study indicate that broad-scale hydrologic modifications affected floodplain forest recruitment and growth but local-scale factors such as topography, canopy disturbances, surface soil moisture, and groundwater mediated these effects.

Date

2012

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

King, Sammy L.

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